a. Field of the Invention
This invention relates to novel ammonium polyphosphates and their preparation; the invention is also concerned with compositions containing such polyphosphates as a flame retardant and to method of retarding flammability.
B. Description of Prior Art
Inorganic phosphorus-containing compounds are known as flame retarding compounds for a variety of substrates, and their use has been reported in various texts and patent disclosures, for example, Flame Retardancy of Polymeric Materials, Vol. 1, Edited by William C. Kuryla and A. J. Papa, 1973, published by Marcel Dekker, Inc., New York.
In particular the use of ammonium phosphates is well known. Such phosphate compounds may be blended in a coating formula or incorporated directly into a polymeric material, for example, polyurethane foam. While specific properties may be required for each particular application it seems generally acknowledged that for adequate flame retardancy the thermal decomposition curve of the flame retarding material must be similar to that of the substrate (W. G. Schmidt, Trans. J. Plastics Inst., December 1965, p. 247; J. A. Rhys, Chem. Ind. (London), 187 (1969)).
The development of various water based coatings has created a need for flame retarding compounds which are compatible with aqueous emulsions of polymers, for example, polyvinyl acetate emulsions. Generally, such compatibility requires that the flame retarding compound exhibit very low hygroscopy and low water solubility. The simple phosphates, for example, monoammoniumorthophosphate are generally water-soluble and hence unsuitable for aqueous emulsions. Furthermore, paint formulations containing water-soluble phosphates compare unfavourably with other paint formulations in washability, colour versatility and storage-ability; also the fire-retardant properties deteriorate with age due to the effect of weather and humidity on the water-soluble phosphate.
An ammonium polyphosphate of low water solubility is described in Canadian Pat. No. 822,594 -- Paul G. Sears et al -- issued Sept. 9, 1969; and this polyphosphate has found use in aqueous emulsions.
In addition to appropriate thermal decomposition and low water solubility other desirable properties or preparation features are desirable. For example, the product should be relatively easy to crush and grind into particles of such size as required for smooth application of coatings. Furthermore, the preparation should be as simple as possible, that is, controllable reactions involving mild conditions and a minimum amount of phases.